1. Field of the Invention
The present invention relates to a photometric apparatus, for use in a camera or the like, operative to measure the luminance in several portions of an objective field and determine the expedient exposure value basing on the measured signals.
2. Description of the Prior Art
Various systems have been proposed as a means for determining the exposure value of a camera and the like by measuring the luminance in several portions of an objective field and setting the exposure value basing on the produced luminance signals. These include the system of determining the exposure value from the average value, mean value or most-frequency value of many luminance signals, the system of determining the exposure value from the maximum or minimum value of many luminance signals shifted by about half of the film latitude, and the system of determining the exposure value from the mean value of the maximum and minimum values of many luminance signals.
A photometric apparatus described in the U.S. Pat. No. 4,476,383 (corresponded to the Japanese Utility Model Publication No. 60-11475) is designed to operate in such a way that several luminance signals are produced for several divided areas in an objective field, an average value of the signals is evaluated, each luminance signal in each area is compared with the mean value so as to standardize the luminance in each divided area, and the exposure value is determined through the pattern analysis using the correlation between patterns and expedient exposure values based on the experiment and experience.
There have been proposed exposure value setting devices, as described in the U.S. Pat. No. 4,456,354 (corresponded to the Japanese Patent Laid-open No. 58-100839) and Japanese Patent Laid-Open Nos. 57-622, in which the spot luminance value in a central portion and an averaged luminance value in peripheral portions are measured to evaluate the brightness of an objective field, and a certain exposure compensation is applied when the difference between the central luminance and peripheral luminance is greater than a preset value.
The above-mentioned prior art photometric apparatus are intended to determine more optimal exposure value through the recognition of the luminance distribution in the entire object field, rather than the determination of the exposure value simply based on an averaged metering or spot metering. However, even in these apparatus, if there is a great difference in brightness between an object portion to be focused and other portions, an over-exposure or an under-exposure for the intended portion would result.
The above-mentioned prior art photometric apparatus implement analog-to-digital conversion of the sensor signals produced for the divided areas in an objective field for the digital calculation in determining the exposure value. Such an analog-to-digital conversion, however, inevitably takes a considerable time for processing the sensor signals. On this account, more quick signal processing has been desired in the photometric apparatus built in cameras or the like where quick, continuous shooting is a prerequisite.